A receiving apparatus for receiving digital broadcasts such as terrestrial digital broadcasts performs frequency conversion and demodulation of a received high-frequency signal to a demodulated frequency. In order to keep the input signal that is inputted to a demodulating circuit in this case constant, gain control is performed as disclosed in Unexamined Japanese Patent Application KOKAI publication No. 2002-290178.
In the case of the receiving apparatus for digital broadcasts, a received analog signal is converted to a digital signal by an ADC (Analog-Digital Converter) to perform demodulation operation; however, operation associated with the gain control is generally performed in an analog circuit before the digital conversion.
In this kind of conventional receiving apparatus, gain control of an IF (Intermediate Frequency) amp, which amplifies using the output frequency that is inputted to a demodulator, amplifies a signal that has been narrowed to the necessary frequency band by a filter. Therefore, by finding the output power of the IF amp, a gain controller in a demodulator can perform suitable gain control. On the other hand, an RF (Radio Frequency) amp performs lumped amplification of a broadcast frequency band, so broadcast signals (unnecessary signals) other than the desired broadcast channel (desired signal) are also amplified. When the gain of an RF amp is excessively high, the output signal becomes saturated and distorted, so by matching the gain of the RF amp with the desired signal, the gain becomes excessive for the unnecessary signal, and the output signal become distorted.
Therefore, in a conventional receiving apparatus, by performing power detection at a stage before the filter, and controlling the gain by using the power of the entire broadcast frequency band and not just that of the desired signal, distortion in the RF amp is avoided. Therefore, in order to perform gain control of an RF amp, a conventional receiving apparatus had to have analog circuits such as a power detector and gain controller.
Here, in order to make a conventional receiving apparatus low cost and compact, a silicon tuner IC is often used. In a silicon tuner IC, the characteristics in the guaranteed temperature range desired for the receiving apparatus change. A silicon tuner IC that is achieved by integrating analog circuits absorbs changes in performance that accompany changes in temperature, so a circuit for assuring the temperature is also necessary. Also, in some cases, there are parts that do not fit within the assured temperature range.